Research, to be conducted on bovine liver UDP-glucose dehydrogenase, will be directed toward the goals of (a) assessing the reactivity of the active site SH group toward alkylating agents, (b) determining whether the feedback inhibitor, UDP-xylose, acts competitively with UDP-glucose or allosterically, and (c) elucidating the nature and stability of quaternary structure interactions. Alkylating agents such as iodoacetate, IAcO ion, and iodocetamide, IAcNH2, rapidly inactivate the enzyme. The former reagent reacts with just one of the 12 SH groups per subunit. The kinetics of these reactions and the reaction with N-ethylmaleimide will be investigated in detail. The IAcO ion treated monoderivatized enzyme will be used in binding studies to determine whether UDP-xylose binds strongly to sites other than the active site. If UDP-xylose does so bind, but UDP-glucose does not bind to the enzyme, the hypothesis that a true allosteric site exists in UDPG-dehydrogenase will be supported. Quaternary structure studies will involve the examination of the dissociation of native hexamers to dimers induced by low concentrations of quanidine hydrochloride as detected by equilibrium centrifugation. Accompanying circular dichroism studies will monitor tertiary structure changes. Enzyme activity studies will be done to correlate quaternary structural integrity with active site function.